Prior semiconductor encapsulating epoxy resin compositions often have blended therein inorganic fillers such as fused silica and crystalline silica. The crystal-line silica is known to have high thermal conductivity and is thus used in applications where efficient heat transfer is required. By increasing the amount of crystalline silica blended, the thermal conductivity of the composition can be increased, but only to an upper limit on the order of 65 cal/cm.multidot.sec.multidot..degree.C. If more crystalline silica is blended to further increase the thermal conductivity beyond this limit, the composition becomes too poor in flow for use in transfer molding.
For further increasing the thermal conductivity of a cured epoxy resin composition, it has been contemplated to use fillers more thermally conductive than crystalline silica, for example, alumina, silicon nitride, aluminum nitride, boron nitride (BN), silicon carbide, and calcium carbonate. These inorganic fillers provide epoxy resin compositions having higher thermal conductivity than crystalline silica filled compositions, but show poor flow and cure into less moisture resistant products. There are no epoxy resin compositions available which possess not only good moldability, but also form cured products having high thermal conductivity and moisture resistance.
Therefore, an object of the present invention is to provide an epoxy resin composition which is readily moldable without substantially forming a fin and which can form a cured product having high thermal conductivity and moisture resistance. Another object of the present invention is to provide a semiconductor device encapsulated with a cured product of such a composition.